This invention is directed to the drying of malt for use in the brewing, distilling, food and other industries and more particularly concerns a method and apparatus for the drying or kilning of malt utilizing fluid bed type dryer units supplied with conditioned air for carrying out a controlled, substantially continuous drying of the malt. Various optional devices are associated with the dryer units to promote energy efficiency in the drying/kilning process and to "brighten", and clean and purify the malt in an environmentally acceptable manner as it passes through the drying zones.
In the drying of malt, it is critically important to achieve both a deliberate drying of the malt and a precise moisture control during the drying process of the temperature in the drying zones so as to develop desired qualities and characteristics in the malt as this will in turn greatly effect the flavor and quality of the end product. Generally, the majority of present day malt drying facilities are of the static or batch-type, employing either single deck kilns or double deck kilns to receive a charge of green malt and having perforated floors allowing air to flow through the malt to effect drying. Malt drying patterns usually proceed in two phase fashion, the first phase being from twelve to seventeen hours of duration at low temperatures, in the range of say approximately 130 to 140 degrees Farenheidt, and with a high rate of air flow, followed by a second phase usually five or more hours in duration at elevated temperatures, ranging approximately from 180 to 185 degrees Farenheidt, with low air flow rates. The exact number of hours in each drying phase, the rate of air flow and temperature of the air employed in any particular instance depend upon a number of different factors, including the variety of malt used and the characteristics desired in the finished malt, among others.
The first drying phase occurs in a single kiln bed for single deck kiln systems and in the upper or top kiln bed of a double deck kiln arrangement. This initial phase, also referred to as the constant rate drying phase, has for its purpose the drying of malt with a beginning moisture content of 40 to 45% to a moisture content of about 8 to 12% during which the moisture removed per unit of time is fairly constant. Moisture removed during this first phase consists generally of unbound surface moisture as well as some bound moisture, that is, moisture exhibiting a vapor pressure lower than pure water and bound to the malt surface by forces such as chemical or physical adsorption, capillary action, solution within cells, etc. After reaching the equilibrium moisture content, i.e. the moisture content at which the water vapor pressure of the malt equals the partial pressure of the water in the ambient air and is independent of temperature in the range of 60 to 100 degrees Farenheit, the next drying phase, also known or referred to as the declining drying rate phase, is usually begun.
In a single deck kilning system, the second phase of drying is begun immediately after the first phase in the same kiln bed or floor. In a double deck kiln system, the first phase is completed in the upper deck and the second phase is completed in the lower deck. The finished malt, having undergone the second phase, is removed from the lower deck or floor, after which the malt in the upper deck, having undergone the first drying phase, is dropped to the lower deck. A new batch of green malt is then loaded into the upper deck to initiate a subsequent drying cycle. The second drying phase is dependent more on increased temperatures rather than air flow to remove the remaining moisture bound within the malt. The goal of the second phase is to acheive a final moisture content of approximately four percent (4%) depending upon the malt variety and desired specifications. The secondary drying phase is also important in developing flavor, color and certain enzyme characteristics important to the end user of the malt.
Single deck kiln systems typically operate on a 24 hour cycle including loading and unloading procedures. Double deck kiln systems typically run on a 48 hour cycle, unloading a finished batch of malt every 24 hours. In a double deck kiln arrangement, the first 12 to 17 hours of drying are part of phase one, primarily drying in the upper deck though some drying may still occur on the lower deck. The next five to six hours of drying are phase two wherein elevated temperatures dry the lower bed while cool air is passed under the upper bed to protect against unnecessary, undesirable enzyme deterioration of the still undried malt in the upper bed.
Other malting systems are available such as partition kilns, combination germination/kilning beds and triple deck kilns, but the trend in North America still is towards single and double deck kilns. Further detailed technical information concerning known malt drying methods can be obtained from organizations such as the Master Brewers Association of America and from technical/specialist literature, including patents such as U.S. Pat. No. 4,982,511, for example.
These conventional batch type kiln dryer arrangements while generally satisfactory from the standpoint of producing a deliberate, controlled drying of the malt are noted as being relatively inefficient insofar as energy technological advances in this area, there is a definite need for more energy efficient systems in the malting industry. This need is prompted in part by the high cost of energy and the public and government concern for energy conservatism in all aspects of business and industry.
In the drying of malt, it is known to subject the malt at one stage or another in the drying process to sulfur dioxide for the purpose of eliminating or reducing naturally occurring carcinogens in the malt by acidifying the surface membrane of the malt grains. Sulfur dioxide also affects the "brightness" or overall finished appearance of the dried malt. Normally, the sulfur dioxide is produced by burning sulfur in open pans and venting the end product to the kilns along with the air being used to dry the malt. A portion of the sulfur dioxide is absorbed by the malt and the rest is vented to the atmosphere. However, present day concerns for air quality and ever increasing governmental regulations concerning pollutants in the atmosphere dictate the need for an improved system for accomplishing this particular aspect of the malt drying and/or preparation process.
Similarily, in some known malt drying and preparation processes, it is known to treat the malt with various pesticides to minimize or eliminate insect infestations in the grains. Here again, increasing environmental concerns have brought about a spate of regulations restricting the use of many pesticides and carefully regulating the permissible manner in which such pesticides may be dispersed. For this reason, increasing attention has been given to the development of alternative techniques for carrying out this phase of the malt drying/preparation process.